C-H activation induced by water. Monocyclometalated to dicyclometalated: Cboolean AND N boolean AND C tridentate platinum complexes

Metalation of 2,6-diphenylpyridine (1) by potassium tetrachloroplatinate in acetic acid gives a monocyclometalated chloride-bridged dimer 4. This dime r is split with CO to give a kinetic product st with the incoming CO trans to the orthometalated carbon. The kinetic product of cleavage is shown to b e 16 kJ mol(-1) higher in energy than the thermodynamic product 9c, which h as the CO trans to the pyridine nitrogen. The isomerization of 9t to 9c is shown not to take place via an associative mechanism and, with analogue 11, is effectively suppressed when excess chloride is added, implying that it takes place via a chloride dissociation. The monocyclometalated 9 undergoes a second cyclometalation to give the C boolean AND N boolean AND C dicyclo metalated complex 15 in high yield. This second cyclometalation is brought about by the simple expedient of adding water to the monocyclometalated pre cursor. The addition of water is rationalized on the basis of needing to io nize the HCl byproduct of the reaction. Using a substituted pyridine (5) an alogous chemistry is observed. Single-crystal X-ray structures of one of th e intermediates (6) and one of the final products (15) have been solved. De nsity functional theory calculations are used to rationalize the isomerizat ions of the monocyclometalated intermediates and the need to ionize HCl in the second cyclometalation.